JP3561729B2 - Digital image forming equipment - Google Patents

Description

同様に、図１６に示すように、液晶パネル１４２’に、ダイヤル１４４、１４６の代わりにレバー１４４’、１４６’を設けてもよい。レバ−１４４’、１４６’を上下して、階調カーブの高濃度と低濃度での段階（＋，０，−）が設定できる。
【００２６】
図１７はさらに別のタブレットエディタ１５０を示し、図１７に示した階調カーブ設定法では、タブレットエディタ１５０に、中心、低濃度、高濃度を設定するキー１５２、１５４、１５６が設けられる。中心キー１５２は、階調カーブがリニアな関係を表す破線と交差する濃度（中心点）Ｐを左右に移動するキーである。低濃度キー１５４は、中心点より低濃度側でカーブを上下するキーである。高濃度キー１５６は、中心点より高濃度側でのカーブを上下するキーである。ここで、低濃度と高濃度では、０を中心として±Ｎ段階の設定が可能である。
【００２７】
図１８はさらに別のタブレットエディタ１６０を示し、図１８に示した階調カーブ設定法では、液晶パネル１６０の上で、ポイントペン（図示しない）を用いて、階調カーブを自由に設定できる。すなわち、原稿濃度の最高値と０の間で任意の折れ点座標１６２を設定可能であり、図の例では４点で設定されている。ここで、折れ点とは、折れ線をつなぐ接点をいい、各折れ点（両端を含む）の間は折れ線で近似される。
【００２８】
（ｇ）階調補正データの演算
本実施例においては、ＡＩＤＣセンサ２１０が検出するトナー付着量を２８のレベルに階層分けし、このレベルに対応して、現像バイアス電位Ｖ_Ｂ、感光体表面電位Ｖ_Ｏ（帯電チャージャ４３のグリット電位Ｖ_Ｇ）を設定する。従って、ＡＩＤＣセンサ２１０のレベルに応じて作像条件が変更されるため、各レベルに応じた作像条件での階調補正データが必要となる。また、複数の階調カーブを選択可能とした場合、例えば、図１０で示した４×３種類の階調補正カーブと標準階調補正カーブの計１３種類の階調補正カーブを選択可能とした場合、各階調補正カーブ毎に、プリント色のＹ、Ｍ、Ｃ、Ｋ及び２８のレベルに対応させて階調補正データを記憶する必要が生じる。即ち、１３×２８×４＝１４５６セットの階調補正データを記憶する必要がある。
しかし、このような多数の階調補正データをすべて記憶するには、後で説明するように折れ線近似を用いたとしても、大きな記憶容量を必要とする。そこで、本実施例では、少数の基本的階調カーブ（元階調カーブ）のみを記憶しておき、選択された階調カーブの形状に応じて、そのつど階調補正データを演算する。これにより、全部の階調補正データを記憶しておく必要がなくなり、メモリ容量を小さくできる。これらのデータは、折れ線近似で記憶すれば、さらに記憶容量を小さくできる。
【００２９】
図１９は、本実施例の階調制御の概念を示すための図である。データＲＯＭ２０３において、補正前の元階調カーブが、ＡＩＤＣセンサ２１０の検出レベルに対応してＣ，Ｍ，Ｙ，ＢＫの各色ごとに２８個記憶されるとともに、図１０に示した４×３＋１＝１３種の設定可能な階調カーブも記憶される。
なお、本実施例においては、元階調カーブとして、ＡＩＤＣセンサ２１０の各レベルにおいて、入力される画像信号の値をリニアに露光量に変換してプリントを行った場合の階調カーブを記憶している。
まず、（Ａ）ユーザが、操作パネル２２１により階調カーブを設定する。なお、設定は、タブレットエディタ２３２で行うようにしてもよい。
一方、（Ｂ）ＡＩＤＣセンサ２１０の検出値レベル１〜２８に対応する元階調カーブを呼び出す。
次に、（Ｃ）呼び出された元階調カーブと設定された階調カーブとから、図９の標準階調カーブの場合と同様な方法で、階調補正データを演算する。
【００３０】
図２０は、この階調補正データの演算の手順を示すグラフである。図２０において、あるＡＩＤＣレベルでの元階調カーブを▲１▼で示す。▲１▼は、画像入力レベルＯＤに対してレーザ露光量をリニアにした（下側の点線で示す直線）場合の非線形な階調カーブであり、ＲＯＭ２０３より呼び出される。また、▲２▼はオペレータによって操作パネル２２１より設定された階調カーブである。次に、この２つの階調カーブ▲１▼▲２▼を用いて、設定された階調カーブ▲２▼を実現するための階調補正データの演算手順について述べる。
画像入力レベルＬ１１の場合について説明する。画像入力レベルＬ１１が与えられた場合、設定された階調カーブ▲２▼では、点Ｃ’で示される画像濃度でプリントする必要がある。この点Ｃ’と同じ画像濃度を再現する元階調カーブ▲１▼上の点は点Ｃ”であり、この点Ｃ”は、レーザの露光量をＰ（Ｌ１１）とすると再現されることが判る。従って、画像入力レベルＬ１１が与えられた時、Ｐ（Ｌ１１）のレーザ露光量でプリントすれば、設定された階調カーブ▲２▼で示された階調特性でプリントが行われることになる。このようにして、他の画像入力レベルについても変換を行い、設定された階調カーブ▲２▼を実現するための、画像入力レベルとレーザ露光量の関係を示す階調補正データ▲３▼を演算する。
（Ｄ）こうして得られた補正カーブは、ＲＡＭ２０４に記憶され、同じ階調の設定が行われるときに再使用される。
以上の説明においては操作パネル２２１より階調カーブが設定される場合について記載したが、他の場合、例えばエディタ２３２、１４０、１５０、１６０の場合であっても、元階調カーブより演算することにより、階調補正データを得ることができる。
【００３１】
（ｈ）プリンタ制御のフロー
図２１は、プリンタ制御部２０１のメインフローを示す。まず、初期設定を行った後（Ｓ１）、操作パネル２２１のキー入力処理を行い（Ｓ２、図２２参照）、操作パネル２２１のスタートキー３０４が押下されるのを待機する（Ｓ３）。スタートキーが押下されると、センサ入力処理が行われる（Ｓ４）。
次に、操作パネル２２１の各種スイッチからの入力信号がプリンタ制御部２０１内のＲＡＭ内に取り込まれる（Ｓ５）。
次に、ステップＳ４およびＳ５で得た設定値によって、図６のゲイン切換回路２５５のゲインを切換えて、半導体レーザ２６４の光量レベルを設定する（Ｓ６）。
【００３２】
次に、ＡＩＤＣ測定処理が実行され、ＡＩＤＣセンサ２１０によりトナー付着量が得られる（Ｓ７）。このＡＩＤＣ処理においては、基準トナー像を感光体上に作像して、その画像パターンのトナー付着量により画像再現濃度を、ＡＩＤＣセンサ２１０によって検出し、プリンタ制御部２０１内のＲＡＭ２０４に取り込む。
次に、測定されたトナー付着量に対応する濃度検出レベルに基づいて、このレベルに対応してあらかじめ設定されているグリッド電位補正値と現像バイアス電位補正値と元階調カーブを選択する（Ｓ８）。
次に、上記ステップＳ８で選択された元階調カーブを基に図２０に示した階調補正データを演算する（Ｓ９）。
次に、上記ステップＳ８にて選択されたグリッド電位Ｖ_Ｇと現像バイアス電位Ｖ_ＢとステップＳ９で演算して得られた階調補正データに基づいて公知の電子写真法によるプリント動作を、終了するまで実行する（Ｓ１０、Ｓ１１）。
なお、カラー画像の場合には、１回の複写は、シアン、マゼンタ、イエロー、ブラックの順で順次処理される。したがって、上述のメインフローは、各色ごとに繰り返される。
【００３３】
図２２は、キー入力処理（図２１Ｓ２）のフローを示す。まず、階調カーブの形状の入力を受け付け（Ｓ２１）、次に、その形状の度合いの入力を受け付ける（Ｓ２２）。最後に、カラーバランススイッチ２１６と操作パネル２２１からカラーバランスと濃度調整値を入力して（Ｓ２３）、リターンする。
【００３４】
図２３は、Ｖ_Ｇ，Ｖ_Ｂ，階調データ選定（図２１Ｓ８）のフローを示す。ＡＩＤＣセンサ２１０の検出値レベルに基づいてグリッド電圧Ｖ_Ｇ，現像バイアス電圧Ｖ_Ｂを選定する（Ｓ４１）。そして、（Ｖ_Ｇ，Ｖ_Ｂ）に対応した元階調カーブを選定して（Ｓ４２）、リターンする。
【００３５】
（ｉ）階調データの折れ線近似
先に説明したように、本実施例では、ＡＩＤＣセンサ２１０のレベルに対応して大量の元階調カーブが必要になる。本実施例では、原稿濃度データとして８ビット（０〜２５５）のデータを用いるが、演算では、精度を落とさないために１０ビット（０〜１０２３）のデータとして扱う。このような階調補正変換のために、階調カーブをルックアップテーブルとして記憶するには、多大なメモリ容量が必要になる。
【００３６】
そこで、本実施例では基本的な元階調カーブや選択可能な階調カーブを折れ線近似を用いて記憶することで、その容量を減らすことができる。
また、選択された階調カーブに対して、元階調カーブより演算された階調補正データも、折れ線近似を用いて記憶すればメモリの容量をさらに減らすことができる。
折れ線近似とは、画像入力レベル（０〜２５５）に対して対応するデータを全て記憶することでなく、例えば、１０〜２０本の直線を折れ線状に結ぎ合わせたもので近似するのである。その際には、各直線の適用範囲係数Ｘ（Ｎ）（Ｎ＝１〜１０）と、その傾き係数ａ（Ｎ）、切片係数ｂ（Ｎ）としてカーブがＲＯＭ２０３に記憶されている。
演算時には、画像入力レベル（０〜２５５）に対して、まず、折れ線で記憶されている元階調カーブと設定された階調カーブとから設定された階調カーブを実現する階調補正データ（入力０〜２５５に対応）が先に説明した通り順次計算され、一旦、入力０〜２５５に対応したデータとしてＲＡＭ２０４に記憶される。これをそのまま階調補正データとしてもよいが、更にこれも折れ線近似した形にすれば保存する時にもメモリ容量を小さくできる。そこで、計算されたデータは、更に２次微分された値の絶対値を基として決められる座標を用いて、折れ線の形にされることが望ましい。
【００３７】
図２４に上側に画像入力レベル（Ｘ）に対する発光データｆ（ｘ）を示し、それの１次微分値ｆ’，２次微分値ｆ”を中央と下側に示す。
２次微分値ｆ”は、いわばｆ（ｘ）の傾きの変化率と呼んでもいいもので、ｆ”（ｘ）の値が大きい箇所は、ｆ（ｘ）の傾きの変化が激しいところと言うことができる。この部分を優先させた形で折れ線近似することで、実際の階調補正の精度を上げることができるのである。
一例を示すと、図２４において、入力レベル０〜２５５に対して、ｆ”≦ｑ、ｆ”≧ｐとなる領域を判別する。そして、例えば折れ線近似の接点数を１０（０を含まず）とした時に、０〜Ｒ領域に４点、Ｓ〜２５５領域に４点、その他２点といったように、あらかじめ決められた優先度に基づいて座標点数が割り振られ、それに応じて、座標は、まず、０〜Ｒを５等分され、Ｘ＝Ｓ，Ｓ＋（２５５−Ｓ）／３、Ｓ＋２×（２５５−Ｓ）／３、２５５、と、Ｘ＝Ｒ＋（Ｓ−Ｒ／３）、Ｒ＋（２×Ｓ−Ｒ／３）の１０点が決定される。それらを原点０と合わせて順次低レベル側から直線で結び、それぞれの対応入力データレベル範囲Ｘ（Ｎ）、傾きａ（Ｎ）、切片ｂ（Ｎ）を求めることで折れ線近似式が作成され、これらをＲＡＭに記憶しておく。
複写動作に入るとイメージリーダ部からの入力濃度データに応じて、対応するａ（Ｎ）、ｂ（Ｎ）から露光出力レベルを求め、その出力に応じてレーザを出力されるのである。
なお、前記の優先度や、ｐ，ｑのとり方は、折れ線座標点数に応じて決定されればよいし、また、ハイライト部を特に優先させるようにしてよい。これらは、機種別に別途設定されてもよい。
【００３８】
２次微分の判定の際は、ｐ，ｑを別途設定してもよいし、｜ｆ”｜としてｐのみで判定してもよい。
優先度に応じてあらかじめ決められた点数に対応した座標決定を説明したが、この他にも、あらかじめ０〜２５５を最終接点数より多くの領域に分割しておき、それに対応した箇所での２次微分結果ｆ”の大きい座標から決定するといったやり方もできる。例えば、４毎にｆ”の値を計算し（ｆ”（４）、ｆ”（８）、ｆ”（１２）、…ｆ”（２５２））それらのうち大きいものから順次、原点０とＭａｘ２５５レベルを除く９点（折れ線１０本で近似の場合）を決定し、それらと０及び２５５を加えて折れ線を作成するというやり方でもいいのである。
このようにして、作成された折れ線近似値をＲＡＭに記憶しておくことで、同じ元階調カーブを選択した時に繰り返し利用することができる。
また、元階調カーブを２０本の折れ線（接点数０を除いて２０点）で近似しＲＯＭに記憶し、これに対し、演算された階調補正データは１０本の折れ線で近似する。
このように元階調カーブの座標点数を実際の演算結果である階調補正データの座標点数より多くすることは、演算の精度向上につながる。
【００３９】
（ｊ）外部記憶装置の利用
階調カーブは、ＩＣカードなどの外部記憶装置から入力できる。図５に示した操作パネル２２１では２個のＩＣカードが挿入口３１１、３１２に挿入できる。
ＩＣカードのメモリ構成は、本体の種類に対応して構成する。
図２５と図２６は、ＩＣカードの外観と内部構成を示す。ここで、ＩＣカード本体１３０には、導電部１３１が印刷されている。この導電部１３１を通じて外部から電源供給が行われ、または、外部とのシリアルインターフェースによりデータの送受信を行うことができる。
ＩＣカード内にある制御ＣＰＵ１３２は、Ｅ^２ＰＲＯＭ１３３の管理および外部とのインターフェース制御を行う。Ｅ^２ＰＲＯＭ１３３にデータが保持される。
【００４０】
図２７は、ＩＣカードに記憶される内部データ１３４の構成を示す。内部データ１３４は、可変長のブロック１３５に分割されている。そして、各ブロックにそれぞれプログラムデータを書き込むことができる。これにより、１枚のＩＣカード内に複数のプログラムを登録することが可能である。
１個のブロック１３５は、以下に説明するような様々なデータから構成される。すなわち、「ヘッダー」には、プログラムの登録／未登録、プログラムの種類を示すコードが入る。「プログラム名」には、プログラムのユーザ登録名称が入り、これを基に、プログラム作成者、プログラムの目的などをユーザが簡単に知ることが可能になる。「機種コード」には、プログラムを作成した機種のコードが入る。「機種特性情報」には、異機種間でＩＣカードを使用するために、プログラムを作成した機種のより詳細な特性情報が入る。「各種モードメモリ」には、操作パネル上で設定可能な様々な複写モードが入る。これを読み出すことにより、このプログラムを作成したときのモード設定状態を忠実に再現することができる。一例として、モードメモリ内には、階調カーブが書いてあり、この階調カーブは、任意の階調カーブ１３６と、複写機本体のＲＯＭ２０３に内蔵している数種類の階調カーブの内のどの階調カーブを選択するかを示すカーブ番号１３７との一方または両方が入っている。
このように機種コードも記憶するようにしたので、ＩＣカードに、挿入可能な機械のコード情報と、それぞれの機械に応じた階調カーブ補正情報を記憶しておくことが可能になる。このため、複数の機械に対して階調データを供給できる。
【００４１】
また、本体のデータＲＯＭ２０３に記憶した階調カーブの外に、ＩＣカードに追加の選択可能な階調カーブを記憶して置き、ＩＣカードの挿入により、ＩＣカードに記憶された追加の階調カーブを、操作パネルに表示させるようにすることができる。多数の階調カーブを記憶するには、大きな記憶容量が必要になるが、機械外部のメモリであるＩＣカードを用いることにより、階調カーブの数を増加できる。このとき、階調カーブは、本体のデータＲＯＭ２０３に記憶したカーブとＩＣカードに記憶したカーブの双方から選択可能である。
複数のＩＣカードに異なる階調カーブを記憶させることにより、さらに階調カーブの数を増加できる。
また、ＩＣカードにＲＡＭを備え、このＲＡＭに本体で作成した階調カーブデータを記憶させる部分を設けることができる。これにより、先に説明したエディタ１６０等で新たに作成した階調カーブをＩＣカードのＲＡＭに記憶しておくことにより、カスタムカードにできる。
【００４２】
図２８は、操作パネル２２１の制御系の構成を示す。パネルＣＰＵ１９０は、各種入出力デバイス１９１〜１９８を制御しながら、操作パネル２２１を統括制御する。また、操作パネル２２１上で設定された複写モードは、インターフェースを通じてプリンタ制御部２０１へ指示信号として送られる。
操作パネル上の操作キー３０２〜３１０、３１３、３１４はキーマトリックスを形成しており、ＯＮ／ＯＦＦの状態は、キーマトリックスを走査することで読み出される。
ＬＣＤインターフェース１９１は、ＬＣＤコントローラ、ビデオＲＡＭ、キャラクタ・ジェネレータなどから構成され、ＣＰＵ１９０から設定された表示データを表示部３０１のＬＣＤモジュール１９２に表示させるためのデータに変換し、ＬＣＤモジュール１９２に表示させる。
ＩＣカードインターフェース部１９３は、２つのＩＣカード挿入口３１１、３１２に対応したＩＣカードユニット（ＩＣカードリーダ／ライタ）１９４、１９５の制御、ＩＣカード挿入の検出、ＩＣカードの排出などを行う。ＩＣカードとは、シリアルインターフェースを通じてデータの送受信を行うため、ＩＣカードインターフェース部１９３でインターフェース制御を行って、ＣＰＵ１９０の負担を軽くしている。
タブレットインターフェース部１９６は、前述したタブレットエディタ２３２あるいは、他のエディタ１４０、１５０、１６０とのデータ送受信制御を行っている。
バーコードインターフェース部１９７は、バーコードリーダペン３１５で読み出され、送られてくるデータを解析し、ＣＰＵ１９０が処理しやすいデータ形式に変換する。
【００４３】
次に、ＩＣカードへの階調カーブの登録について説明する。図２９は、ＩＣカード内にプログラムされたデータを呼び出すための表示部３０１の画面を示す。この画面は、ＩＣカードが挿入された時および操作パネル２２１のプログラム呼び出しキー（図示しない）が押された時に表示される。そして、この画面内には、ＩＣカード内に登録可能な全８種類のプログラムの内、現在登録されているプログラムが画面左部に番号およびタイトル付きで表示され、逆に、未登録のものは、枠だけが表示される。そして、プログラムを呼び出す場合は、その呼び出したい場所にカーソルキー３０９によって選択カーソルを移し、操作パネル２２１のエンターキー３０７を押せばよい。
次に、ＩＣカード内にプログラムを登録する場合には、図２９の画面右部にある「プログラム登録」を選択し、エンターキー３０７を押す。そうすると、図３０に示すタイトル入力画面になる。この画面で、タイトルを入力し、最後に「終了」を選択してエンターキー３０７を押すと、次に、図３１に示すプログラム登録場所の選択画面となる。ここで登録したい場所に選択カーソルを移動し、エンターキー３０７を押すと、その場所に番号およびタイトルが追加され、プログラム登録が完了したことを示す。ここで、プログラムされる内容は、その時の複写機のモード設定内容の全てである。そして、次回にそのプログラム登録したプログラムを呼び出すと、そのプログラムを登録した時と全く同じ状態を再現できることになる。
また本実施例では、２つのＩＣカードを同時に使用可能であるが、いずれのＩＣカードにおいても、プログラムの呼び出し／登録の方法は同じである。
【００４４】
次に、ＩＣカードからの階調データの選択について説明する。
図３２は、ＩＣカードが１つセットされたときの階調カーブ選択画面を示す。ＩＣカード内には、ユーザが作成した任意の階調カーブが１プログラムごとに８種類登録できる。そして、この画面では、ユーザは、その内の４種類と本体標準の５種類の計９種類の階調カーブから選択できる。
図３３は、ＩＣカードが２つセットされたときの階調カーブ選択画面を示す。この画面では、各ＩＣカード内に登録されている階調カーブの内、各４種類がメニュー表示され、その中から階調カーブを選択することができる。
【００４５】
図３４は、バーコードによる入力例を示す。図３４に示されるバーコードは、左から、それぞれ、花、人物、果物、カラー文字、暗い絵といった５種の画質のサンプルの下に付してあり、ユーザは、サンプルの下のバーコードを読み取らせることにより、選択した画質に対応した階調カーブを設定できる。
さらに、図３５に示すように、ＩＣカード１３０にサンプル図（この例では風景画）を付けてもよい。これにより、ユーザによる画質の選択が容易になる。
【００４６】
【発明の効果】
目標の階調カーブ数Ｎと画像濃度制御数Ｍがあると、Ｎ×Ｍの階調カーブ数が各色に応じて必要になる。これを折れ線近似などで記憶容量を減じても、大きな記憶容量が必要になる。しかし、本発明では、階調補正カーブを目標のカーブデータと基本階調データよりそのつど演算して発光補正データを算出するため、大きな記憶容量を必要としない。
複写装置全体の階調特性のずれに対しては、基本の階調特性データを切り替えることで微調整が可能になる。
全階調特性データを記憶しないで、制御時に演算して求めることにより、記憶容量を大幅に小さくできる。
たとえば、階調特性を折れ線近似で記憶することにより、記憶容量を大幅に小さくできる。外部メモリに追加の目標階調カーブを記憶させることにより、選択の範囲が広がる。異なった機械に対応する階調変換機能を提供することが可能になる。新たに作成した階調カーブを外部のメモリカードに記憶しておくことにより、カスタムカード化できる。
【図面の簡単な説明】
【図１】デジタルカラー複写機の全体構成を示す断面図である。
【図２】画像信号処理部のブロック図である。
【図３】プリンタ制御部の一部のブロック図である。
【図４】プリンタ制御部の一部のブロック図である。
【図５】操作パネルの斜視図である。
【図６】プリンタ制御部における画像データ処理のブロック図である。
【図７】感光体ドラムのまわりの帯電チャージャと現像器の配置を図式的に示す図である。
【図８】反転現像におけるセンシトメトリの図である。
【図９】標準の階調補正データの求め方を示す図である。
【図１０】目標の階調カーブの形状とその形状変化の段階の概念を図式的に示す図である。
【図１１】階調カーブの種類選択の画面の図である。
【図１２】階調カーブのレベル選択の画面の図である。
【図１３】タブレットエディタのパネルの図である。
【図１４】低濃度と高濃度でのダイヤル設定による階調カーブの入力装置である。
【図１５】図１０のダイヤル設定により選ばれる階調カーブを示す図である。
【図１６】低濃度と高濃度でのダイヤル設定による階調カーブの入力装置である。
【図１７】中心、低濃度、高濃度を設定するキーを用いた入力装置の図である。
【図１８】任意の折れ点座標で設定が可能である入力法を示す図である。
【図１９】発光データ演算用に記憶されるデータを示す図である。
【図２０】発光データの演算を示す図である。
【図２１】プリンタ制御部のメインフローの図である。
【図２２】キー入力処理のフローチャートである。
【図２３】Ｖ_Ｇ，Ｖ_Ｂ，階調選定のフローチャートである。
【図２４】上側に発光データを、この発光データの１次微分値と２次微分値を中央と下側に示す図である。
【図２５】ＩＣカードの外観の図である。
【図２６】ＩＣカードの内部構成の図である。
【図２７】ＩＣカードに記憶される内部データの構成を示す図である。
【図２８】操作パネルの制御系の構成の図である。
【図２９】ＩＣカード内の登録プログラムの表示画面の図である。
【図３０】タイトル入力画面の図である。
【図３１】プログラム登録場所の選択画面の図である。
【図３２】階調カーブ選択画面の１例の図である。
【図３３】階調カーブ選択画面の１例の図である。
【図３４】バーコードによる入力例を示す図である。
【図３５】サンプル図を付したカードの図である。
【符号の説明】
２０１…プリンタ制御部、 ２０３…データＲＯＭ、 ２０４…ＲＡＭ、
２１０…ＡＩＤＣセンサ、 ２３２…タブレットエディタ、
２５３…γ補正部、 ３１１、３１２…ＩＣカード挿入口、
３２２，３２３…モード設定キー。[0001]
[Industrial applications]
The present invention relates to gradation control of a digital image forming apparatus in a digital printer, a digital copying machine, and the like.
[0002]
[Prior art]
2. Description of the Related Art In an electrophotographic process in a digital printer, a digital copying machine, or the like, an image is reproduced by modulating laser light emission in accordance with a document reading density (multi-value digital value). In image reproduction, it is desirable that the density of the output image is proportional to the original reading density (digital value). The gradation characteristic, which is the relationship between the output image density and the original reading density, is a factor that largely affects the impression of a pictorial image.
Therefore, the input document density is processed, and the light emission characteristics are corrected so that the density of the formed image is proportional to the input document density. This is called gradation correction. In color image reproduction, it is basically required that the output image linearly changes to the document density, and therefore, image stabilization is required.
The gradation characteristics are delicately changed due to changes in the photoconductor sensitivity, surface potential, development bias potential, development characteristics, and the like in the electrophotographic process. Therefore, image reproduction is stabilized by automatic density control, gradation correction, and the like.
In a digital image forming apparatus, the read document density is converted into a multi-valued digital value. However, since the non-linear conversion of the multi-valued data is easy by a look-up table process or the like, the digital image forming apparatus requires various stable values. (For example, an apparatus described in Japanese Patent Application Laid-Open No. 3-271664 by the present applicant).
[0003]
[Problems to be solved by the invention]
However, in reality, since image stabilization is not perfect, the quality of a reproduced image by stabilization control may not be satisfactory for some professional users.
If the user can arbitrarily select a gradation characteristic as a function of a digital equalizer, the user can realize a desired image tone.
Therefore, it is considered that if the user can actively change the gradation characteristics, the user can be satisfied.
In order to allow the user to change the gradation characteristics, it is necessary to operate the gradation correction and the image stabilization system in conjunction with each other, and a process control system corresponding to each image generation process is required.
Therefore, the present inventor has proposed a digital image forming apparatus in which a user can change gradation characteristics.
However, in such an apparatus, there is a problem that as the number of gradations to be realized increases, the number of gradation data to be stored becomes very large. Therefore, it is desirable to reduce the storage capacity of the gradation data.
[0004]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a digital image forming apparatus in which a user can arbitrarily change gradation characteristics and reduce the storage capacity of gradation characteristic data.
[0005]
[Means for Solving the Problems]
A digital image forming apparatus according to the present invention is a digital image forming apparatus that forms an image based on an input image signal. Concentration level When Printed out actually Shows relationship with image density Non-linear Storage means for storing basic tone characteristics; This is the relationship between the density level of the input image signal and the density of the image actually printed out by the user's operation. Setting means for setting a target gradation characteristic, and a basic gradation characteristic stored in the storage means When , From the set target gradation characteristics, Input Image signal Output level for print output for different density levels And a gradation correction means for converting and outputting an image signal to be formed based on the gradation correction data obtained by the calculation means. And
[0006]
[Action]
In the digital image forming apparatus according to the present invention, the electrophotographic image reproduction conditions selected by the image density control system include, for example, the photoconductor surface potential (V _G ), Developing bias potential (V _B ), Laser emission intensity. Further, conditions relating to variations in the apparatus, changes in the durability of the apparatus, environmental changes, and lots of the developer may be added. The conditions for forming these digital images are set so as to stabilize the image, and the process gradation data (basic gradation characteristics) is selected by the image density control system. At the time of the process control selected by the image density control system (V _B , V _G The process gradation data (basic gradation characteristics) before the correction of the change) is stored in the storage unit. On the other hand, the target gradation curve stored in the storage means can be set by the user. The present apparatus has a gradation correction calculation function, and calculates gradation data from a set target gradation curve and process gradation data.
As the process gradation data before the correction, a gradation correction curve (the fourth quadrant of the sensitometry in FIG. 8) is most preferable. It may be a combination with development characteristics (second quadrant of sensitometry in FIG. 8 + third quadrant).
For example, the target gradation curve and the process gradation data for calculating the gradation correction characteristics can be stored by a polygonal line approximation to reduce the storage capacity. At the time of the calculation by the gradation correcting means, the data is converted from the data of the broken line approximation to the original data, and the calculation is performed using the value.
[0007]
【Example】
Hereinafter, embodiments of the present invention will be described in the following order with reference to the drawings.
(A) Configuration of digital color copier
(B) Printer control unit and image signal processing
(C) Image stabilization
(D) Gradation control
(E) Tone selection
(F) Other gradation selection
(G) Calculation of gradation correction data
(H) Printer control flow
(I) Line approximation of gradation data
(J) Use of external storage device
[0008]
(A) Configuration of digital color copier
FIG. 1 is a cross-sectional view showing the entire configuration of a digital color copying machine according to an embodiment of the present invention. Digital color copying machines are broadly divided into an image reader unit 100 for reading a document image and a printer unit 200 for reproducing an image read by the image reader unit.
The scanner 10 of the image reader unit 100 includes an exposure lamp 12 for irradiating a document, a rod lens array 13 for condensing light reflected from the document, and a contact type CCD sensor 14 for converting the condensed light into an electric signal. It has. The scanner 10 is driven by a motor 11 at the time of reading a document, moves in the direction of the arrow (sub-scanning direction), and scans the document placed on the platen 15.
As shown in FIG. 3, the image reader unit 100 is controlled by an image reader control unit 101. The image reader control unit 101 controls the exposure lamp 12 via the drive I / O 103 according to a position signal from the position detection switch 102 indicating the position of the document on the platen 15, and also controls the drive I / O 103 and the parallel I / O 103. The scan motor driver 105 is controlled via O104. The scan motor 11 is driven by a scan motor driver 105.
[0009]
Referring back to FIG. 1, the image on the document surface irradiated by the exposure lamp 12 is photoelectrically converted by the CCD sensor 14. The multi-valued electrical signals of the three colors red (R), green (G), and blue (B) obtained by the CCD sensor 14 are read by the read signal processing unit 20 into yellow (Y), magenta (M), and cyan ( The data is converted into 8-bit gradation data of either C) or black (K) and output to the printer control unit 201. As shown in FIG. 3, the image control unit 106 is connected to each of the CCD color image sensor 14 and the image signal processing unit 20 via a bus. An image signal from the CCD color image sensor 14 is input to an image signal processing unit 20 and processed.
As shown in FIG. 2, in the image signal processing unit 20, the image signal photoelectrically converted by the CCD sensor 14 is converted by the A / D converter 21 into R, G, B multi-value digital image data. Then, shading correction is performed in the shading correction circuit 22, respectively. Since the image data subjected to the shading correction is the reflected light data of the original, the log data is converted by the log conversion circuit 23 into density data of an actual image. Further, the under color removal / black printing circuit 24 removes unnecessary black color development and generates true black data K from R, G, B data. Then, the masking processing circuit 25 converts the data of the three colors R, G, and B into data of the three colors Y, M, and C. The density correction processing for multiplying the Y, M, and C data thus converted by a predetermined coefficient is performed by the density correction circuit 26, and the spatial frequency correction processing is performed by the spatial frequency correction circuit 27. Output as a density signal.
[0010]
Returning to FIG. 1, in the printer unit 200, the print head unit 31 performs tone correction according to the tone characteristics of the photoconductor on the input image data, and then performs the corrected image processing. The data is D / A converted to generate a laser diode drive signal, and the semiconductor laser 264 (FIG. 4) is caused to emit light by the drive signal.
The laser beam generated from the print head unit 31 by modulating the light emission intensity in accordance with the image data passes through the polygon mirror, passes through the reflecting mirror 37, and exposes the photosensitive drum 41 that is driven to rotate. The photosensitive drum 41 is irradiated by an eraser lamp 42 before being exposed for each copy, and is uniformly charged by a charging charger 43. When exposure is performed in this state, an electrostatic latent image of the document is formed on the photosensitive drum 41. Only one of the cyan, magenta, yellow, and black toner developing units 45a to 45d is selected to develop the electrostatic latent image on the photosensitive drum 41. On the other hand, the copy paper is fed from a paper cassette 50 and wound on a transfer drum 51. The developed toner image is transferred to copy paper by a transfer charger 46.
The above printing process is repeatedly performed for four colors of yellow (Y), magenta (M), cyan (C), and black (K). At this time, the scanner 10 repeats the scanning operation in synchronization with the operations of the photosensitive drum 41 and the transfer drum 51. Thereafter, the copy paper is separated from the transfer drum 51 by operating the separation claw 47, is fixed through the fixing device 48, and is discharged to the discharge tray 49.
[0011]
(B) Printer control unit and image signal processing
FIGS. 3 and 4 are block diagrams showing the entire control system of the digital color copying machine. The printer unit 200 includes a printer control unit 201 that controls general printing operations.
A printer control unit 201 having a CPU is connected to a control ROM 202 storing a control program, a data ROM 203 storing various data (such as gradation correction data), and a RAM 204. The printer control unit 201 controls the printing operation based on the data in the ROM and RAM.
The printer control unit 201 ₀ Analog signals from the sensor 44, the AIDC sensor 210, the ATDC sensor 211, the temperature sensor 212, and the humidity sensor 213, and signals from the fog input switch 214, the color balance switch 216, and the photoconductor lot switch 218 are input. Where V ₀ The sensor 44 detects the potential of the photoconductor surface. Further, the AIDC sensor 210 uses the standard image forming condition (photoconductor surface potential V) for each color. ₀ , Developing bias potential V _B , Exposure amount), the amount of toner of the reference toner image on the photoreceptor developed by ₀ , V _B , Set the exposure amount to the optimum condition.
Various data are input to the printer control unit 201 from a panel CPU 190 that receives a key input or the like from an operation panel 221 described later.
Similarly, input values in a tablet editor 232 (see FIG. 13), which will be described in detail later, are also input to the printer control unit 201 via the panel CPU 190.
[0012]
The printer control unit 201 controls the copy control unit 231 in accordance with the contents of the control ROM 202 according to various input data, and further controls the grid potential V of the charging charger 43 via the parallel I / O 241 and the drive I / O 242. _G V that generates _G Developing high potential unit 243 and developing bias potential V of developing units 45a to 45d _B V that generates _B The generation high pressure unit 244 is controlled.
The printer control unit 201 is also connected to the image signal processing unit 20 of the image reader unit 100 by an image data bus, and will be described later based on an image density signal input via the image data bus. The light emission level is determined with reference to the contents of the data ROM 203 storing the gradation correction table, and the semiconductor laser driver 263 is controlled via the drive I / O 261 and the parallel I / O 262. The light emission of the semiconductor laser 264 is driven by the semiconductor laser driver 263. The gradation expression is performed by modulating the emission intensity of the semiconductor laser 264.
[0013]
FIG. 5 shows the appearance of the operation panel 221. Here, the LCD display unit 301 displays the mode set by the operation, explains the operation procedure to the user, and displays a status such as a jam display or a copy operation display.
The panel reset key 302 is a key for initializing all modes.
A key 303 is a numeric key for setting the number of copies and a clear key for clearing.
A start key 304 is a key for instructing the start of copying.
When the image quality menu key 305 is pressed, a menu for adjusting the image quality is displayed on the LCD display unit 301. The user can adjust the image quality by operating this.
When a create menu key 306 is pressed, a setting menu for various create functions is displayed on the LCD display unit 301. The user can perform various function settings and mode settings by operating this.
An enter key 307 is used as an enter key and a next screen key in each operation screen of the image quality menu and the create menu.
The reverse key 308 is used as a cancel key and a previous screen key.
A cursor key 309 is a key for selecting a menu cursor and setting a level on each operation screen.
The multi-function key 310 is a key whose meaning can be changed by each selection menu displayed on the LCD display unit 301.
This panel has IC card insertion ports 311 and 312, and up to two IC cards can be inserted at the same time. A program call / registration key 313 and an IC card ejection key 314 are provided corresponding to each insertion slot.
Note that the bar code can be read using the bar code reader pen 315 to perform various mode settings.
[0014]
FIG. 6 is a block diagram of image data processing in the printer control unit 201. Here, the image data (8 bits) from the image signal processing unit 20 is input to a first-in first-out memory (hereinafter, referred to as a FIFO memory) 252 via the interface unit 251. The FIFO memory 252 is a line buffer memory capable of storing gradation data of a predetermined number of rows of images in the main scanning direction, and absorbs a difference in operation clock frequency between the image reader unit 100 and the printer unit 200. It is provided in order to. Next, the data in the FIFO memory 252 is input to the gamma correction unit 253. Various gamma correction data in the data ROM 203 is sent to the gamma correction unit 253 by the printer control CPU 250, and the gamma correction unit 253 corrects the input data and sends the light emission level to the D / A conversion unit 254. The data ROM 203 stores various tone correction data. The analog voltage converted from the light emission level (digital value) by the D / A conversion unit 254 is then input to the gain switching unit 255 in accordance with the gain setting value from the printer control unit 201. (Corresponding to different powers P1, P2,...) Are switched and amplified by a set gain, and then sent to a semiconductor laser driver 263 via a drive I / O 261 to receive a semiconductor laser 264. At the light intensity of that value.
On the other hand, the printer control CPU 250 sends a signal to the clock switching circuit 257 to select the clock generation circuit 258 or 259, and sends a clock signal generated by the clock generation circuit to the semiconductor laser driver 263 via the parallel I / O 262. The image data is modulated by the clock. By selecting the clock generation circuit, the duty ratio (pattern) of the light-emitting signal is changed (for example, 100% and 80%), and the reproducibility of gradation can be selected. When the duty ratio is 100%, the light emission corresponds to normal light emission. When the duty ratio is 80%, light emission is performed during a period of 80% of the normal light emission period.
[0015]
(C) Image stabilization
The gradation characteristics basically include the sensitivity characteristics, development characteristics, and charging potential V of the photoconductor. ₀ , Developing bias potential V _B , The attenuation potential V of the electrostatic latent image _S Is determined by the setting. In color image reproduction, it is basically required that the density of an image (output image) to be formed linearly changes to the density of a document, and therefore, image stabilization is required. Although the present invention allows a user to select a gradation characteristic, a gradation control system operates in conjunction with an image stabilization system and can always supply the selected gradation characteristic stably. Must be something.
[0016]
Before describing image stabilization, an outline of the electrophotographic process will be described. FIG. 7 schematically shows the arrangement of the charging charger 43 and the developing unit 45r around the photosensitive drum 41. Here, the photoconductor 41 has a discharge potential V _G Are placed facing each other. A negative grid potential V is applied to the grid of the charger 43 by the grid potential generating unit 243. _G Is applied. Grid potential V _G And the surface potential V of the photosensitive drum _O Is approximately V _O = V _G Therefore, the potential V on the surface of the photosensitive drum 41 is ₀ Is the grid potential V _G Can be controlled by Note that the surface potential V _O Is the surface voltmeter V _O It is detected by the sensor 44.
First, before laser exposure, a negative surface potential V is applied to the photosensitive drum 41 by the charging charger 43. _O However, the developing bias generating unit 244 applies a low negative developing bias potential V to the roller of the developing unit 45r. _B (| V _B | <| V _O |) Is given. That is, the developing sleeve potential of the developing device 45r is V _B It is.
The potential of the irradiation position on the photosensitive drum 41 is reduced by the laser exposure, and the surface potential V _O From the decay potential V of the electrostatic latent image _S Transitions to Decay potential V _S Is the developing bias potential V _B When the potential becomes lower than that, the negatively charged toner carried to the surface of the sleeve of the developing device 45r adheres to the photosensitive drum 41.
[0017]
Where V _O And V _B If the difference is too large, the carrier adheres to the non-exposed area, and if the difference is too small, toner fog occurs. Therefore, the difference may not be too large or too small. The toner adhering amount is determined by a developing potential difference ΔV = | V _B -V _S The larger | is, the more. On the other hand, the decay potential V _S Indicates that the surface potential V _O It changes as changes. Then, V _O And V _B Of the surface potential V while maintaining the difference within a certain range, for example, while keeping the difference constant. _O And developing bias potential V _B Changes, V _B And V _S , The amount of toner adhered can be changed, and the density can be controlled (see, for example, Japanese Patent Application Laid-Open No. 3-271664).
The gain of laser emission is V ₀ Switching is performed according to sensitivity information of the photoconductor obtained by the sensor 44.
[0018]
Further, the electrophotographic process is affected by the environment because it handles static electricity. Therefore, mainly the development characteristics and the photoconductor characteristics change, so this compensation is necessary. Therefore, the amount of toner attached to the reference toner image developed under the standard image forming conditions is detected by the AIDC sensor 210 for each of the four colors. That is, a reference toner image, which is the basis of density control, is formed outside the image area on the photosensitive drum 41, and the toner amount is detected by the AIDC sensor 210 provided near the photosensitive drum 41. In correspondence with this detection value, the developing bias potential V _B And grid potential V _G And the developing potential difference (ΔV) is selected to perform automatic density control for keeping the toner adhesion amount at the maximum density level constant. Also, background fog must be removed.
[0019]
(D) Gradation control
Next, a description will be given of standard tone correction in which the value of an input image signal and the density of an actually printed image are linear. Particularly, a color image is required to have basically linear characteristics. FIG. 8 is a diagram of sensitometry in reversal development. The value of the image signal (image input level OD) input from the image reader is output linearly with respect to the document density. When the laser emission amount P (Lx) is linearly changed with respect to the image input level value Lx, the gradation characteristic (the relationship between the actually printed image density (output image density ID) and the image input level OD) becomes Becomes nonlinear.
In response to laser emission, the surface potential V of the photoreceptor _S Decays. That is, as the laser light emission amount increases, the surface potential gradually decreases nonlinearly. Further, the developing bias potential V _B Is the photoconductor charging potential V so that the background fog is removed. ₀ And the development potential difference (V _B -V _S (Lx)) corresponding to the output image density ID (V _S ) Is obtained, but this development characteristic also shows non-linearity. Therefore, instead of linearly changing the light emission amount P of the laser, the respective non-linearities of the photoconductor characteristics and the development characteristics are corrected so that the output image density becomes linear with respect to the input level, which will be described later. As described above, the light emission characteristics are nonlinearly corrected. This allows the output image density to be linear with respect to the image input level.
[0020]
FIG. 9 is a diagram showing how to obtain gradation correction data having standard gradation characteristics for making the output image density ID linear with respect to the image input level OD. When the image input data is directly converted to laser exposure as shown on the lower side without any conversion and exposed, the gradation curve shown on the upper side (the relationship between the output image density and the image input level) is shown as a broken line. Becomes nonlinear. The emission characteristic for converting this into the target gradation curve shown by the solid line is the curve shown by the solid line in the figure. That is, point A (image input level L) on the dotted line in FIG. ₁ ) To the point A 'on the solid line, the laser exposure amount P (L) at the point A "on the broken line having the same output image density as the point A' ₁ ) Is input image data L ₁ Should be output in response to. Similarly, in order to convert point B on the dotted line to point B 'on the target solid line, the laser exposure amount P (L) at point B "on the broken line having the same output image density as point B' ₂ ) Should be output. In this way, the laser exposure amount corresponding to the image input level, that is, the gradation correction data is obtained.
[0021]
(E) Tone selection
In the above, a description has been given of realizing a standard gradation curve for outputting an image density linearly with respect to input image data in order to obtain an output faithful to a document image.
In this embodiment, the user can select a different gradation curve in addition to the standard linear gradation curve.
In the present embodiment, in order to select a gradation curve, in order to facilitate selection by a user, the gradation curve is designated by inputting in two levels of a gradation curve shape and a degree of change in the shape.
[0022]
FIG. 10 schematically shows the concept of the shape of the target gradation curve and the degree of the change in the shape. The following four types (a) to (d) can be considered as combinations of selection of the gradation curve based on the relative relationship with the standard gradation curve. By changing the degree of change of each shape, an infinite gradation curve can be realized.
In the low-density emphasis type (a), the gradation curve is convex upward. Using this gradation curve gives a solid feeling.
In the high density emphasis type (b), the gradation curve is made convex downward. By using this gradation curve, a pastel tone can be obtained. Also, it is possible to correct a dark image as a whole.
In the halftone density portion enhancement type (c), the gradation curve has a large upward convex on the high level side, but has a small downward convex on the low level side. When this gradation curve is used, a feeling such as “colorful” or “sharp” is obtained.
In the halftone density portion non-emphasized type (d), the gradation curve is small and convex upward on the low level side, but largely convex downward on the high level side. By using this gradation curve, a feeling such as "moist" or "smooth" can be obtained.
The point where the gradation curves of the halftone density portion emphasized type (c) and the halftone density portion non-emphasized (d) intersect a linear straight line may be the same as, for example, the case of the standard gradation curve (FIG. 8). .
[0023]
Next, a specific method of selecting these gradation curves will be described.
First, selection of a gradation curve by the operation panel 221 shown in FIG. 5 will be described. In the setting of the operation panel 221, the selection is made by two-stage input of selection of the gradation curve and the degree of change of the shape.
First, a screen for selecting a gradation curve is called on the display unit 301 by operating the key 306. FIG. 11 is a diagram of a selection screen displayed on the display unit 301. On the selection screen, the standard gradation curve and each type of gradation curve shown in FIG. 10 are words representing the characteristics of the gradation curve (“standard”, “smooth”, “colorful”, “bright” , "Heavy"). A desired gradation curve is selected from the displayed five gradation curves by a key 310 provided below the display unit 301. When one of the gradation curves is selected by the key 310, words ("weak", "standard", "strong") indicating the degree of change of the gradation curve are displayed on the display unit as shown in FIG. Displayed at 301. The user sets the degree of change by selecting one of them with the key 310 as before. In other words, three levels can be selected for the degree of change. When “strong” is selected, the gradation curve shape of the type selected in FIG. 11 described above, and the gradation farthest from the standard gradation curve shown in FIG. When a tone curve is selected and "weak" is selected, a tone curve closest to the standard tone curve is selected, and when "standard" is selected, an intermediate tone curve is selected.
[0024]
In the above selection, after selecting the type of the desired gradation curve, a display prompting the input of the level of the gradation curve is output. When no level is input, the standard target curve is selected at the level “0”. Is done.
The gradation curve can also be selected by the tablet editor 232 shown in FIG. FIG. 13 shows the appearance of the tablet editor 232. In the coordinate input unit 320, the position on the document can be designated by pointing using the coordinate input pen 321. As a result, partial editing designation of various editing functions can be performed. The coordinate input unit 320 is provided with key groups 322 and 323 for mode setting. That is, the mode setting keys 322 and 323, the gradation curve setting section 324, and the color pallet 325 are printed on the coordinate input section 320, and can be used as a mode setting section and a level setting section by a setting function.
The mode setting keys 322 and 323 are keys for setting various modes, respectively, and can be set by pressing them with the coordinate input pen 321. Therefore, it is also possible to select the type and degree of the gradation curve using the key groups 322 and 323.
[0025]
(F) Other gradation selection
The method of selecting a standard gradation curve and another gradation curve by designating the shape and the degree of change of the curve has been described above. However, setting the gradation curve is not always easy for the user. Therefore, the setting by the user must be facilitated. Hereinafter, other various gradation curve setting methods will be described.
In the example shown in FIG. 14, the shape of the gradation curve can be switched between the high density side (H) and the low density side (L) of the input image density (OD). That is, by adjusting the low density level and the high density level, which are easy for the user to image, the gradation characteristics can be easily selected.
FIG. 14 is an external view of a tablet editor 140 that can be used in place of the tablet editor 232 of FIG. 13 described above.
As shown in FIG. 14, in the tablet editor 140, dials 144 and 146 provided for high density (H) and low density (L) are provided below a liquid crystal panel 142 for displaying a gradation curve. By setting the dials 144 and 146 to one of three levels of + (H), 0, and-(L), a gradation curve is selected. (1) to (9) in FIG. 15 indicate gradation curves selected by the dial setting (see Table 1).
[Table 1]

Similarly, as shown in FIG. 16, the liquid crystal panel 142 'may be provided with levers 144' and 146 'instead of the dials 144 and 146. By raising and lowering the levers 144 'and 146', the steps (+, 0,-) at the high density and the low density of the gradation curve can be set.
[0026]
FIG. 17 shows still another tablet editor 150. In the gradation curve setting method shown in FIG. 17, keys 152, 154, and 156 for setting the center, low density, and high density are provided in the tablet editor 150. The center key 152 is a key for moving the density (center point) P at which the gradation curve intersects a broken line indicating a linear relationship to the left and right. The low density key 154 is a key for moving up and down a curve on the low density side from the center point. The high density key 156 is a key for moving up and down a curve on the high density side from the center point. Here, at low density and high density, setting of ± N steps around 0 is possible.
[0027]
FIG. 18 shows still another tablet editor 160. In the gradation curve setting method shown in FIG. 18, the gradation curve can be freely set on the liquid crystal panel 160 by using a point pen (not shown). That is, arbitrary break point coordinates 162 can be set between the maximum value of the document density and 0, and in the example shown in the figure, four break points are set. Here, a break point refers to a contact point connecting the broken lines, and a portion between each broken point (including both ends) is approximated by a broken line.
[0028]
(G) Calculation of gradation correction data
In this embodiment, the toner adhesion amount detected by the AIDC sensor 210 is hierarchically divided into 28 levels, and the developing bias potential V _B , Photoconductor surface potential V _O (Grit potential V of charging charger 43 _G ) Is set. Therefore, since the image forming conditions are changed according to the level of the AIDC sensor 210, gradation correction data under the image forming conditions corresponding to each level is required. When a plurality of gradation curves can be selected, for example, a total of 13 gradation correction curves of 4 × 3 kinds of gradation correction curves and a standard gradation correction curve shown in FIG. 10 can be selected. In this case, it is necessary to store the gradation correction data corresponding to the Y, M, C, K, and 28 levels of the print color for each gradation correction curve. That is, it is necessary to store 13 × 28 × 4 = 1456 sets of gradation correction data.
However, storing all of such a large number of tone correction data requires a large storage capacity even if polygonal line approximation is used as described later. Therefore, in this embodiment, only a small number of basic tone curves (original tone curves) are stored, and tone correction data is calculated each time according to the shape of the selected tone curve. Thus, it is not necessary to store all the gradation correction data, and the memory capacity can be reduced. If these data are stored in a polygonal line approximation, the storage capacity can be further reduced.
[0029]
FIG. 19 is a diagram illustrating the concept of gradation control according to the present embodiment. In the data ROM 203, 28 original tone curves before correction are stored for each of the colors C, M, Y, and BK corresponding to the detection levels of the AIDC sensor 210, and 4 × 3 + 1 = 4 × 3 + 1 shown in FIG. 13 types of settable gradation curves are also stored.
In the present embodiment, as the original tone curve, a tone curve in the case where printing is performed by linearly converting the value of an input image signal into an exposure amount at each level of the AIDC sensor 210 is stored. ing.
First, (A) the user sets a gradation curve using the operation panel 221. The setting may be performed by the tablet editor 232.
On the other hand, (B) the original gradation curve corresponding to the detection value levels 1 to 28 of the AIDC sensor 210 is called.
Next, (C) tone correction data is calculated from the called original tone curve and the set tone curve in the same manner as in the case of the standard tone curve in FIG.
[0030]
FIG. 20 is a graph showing a procedure for calculating the gradation correction data. In FIG. 20, an original tone curve at a certain AIDC level is indicated by (1). {Circle around (1)} is a non-linear gradation curve when the laser exposure amount is linear with respect to the image input level OD (a straight line indicated by a lower dotted line), and is called from the ROM 203. Further, (2) is a gradation curve set by the operator from the operation panel 221. Next, a procedure of calculating gradation correction data for realizing the set gradation curve (2) using the two gradation curves (1) and (2) will be described.
The case of the image input level L11 will be described. When the image input level L11 is given, it is necessary to print at the image density indicated by the point C 'in the set gradation curve (2). The point on the original tone curve (1) that reproduces the same image density as that of the point C 'is a point C ", and this point C" can be reproduced when the laser exposure amount is P (L11). I understand. Therefore, when the image input level L11 is given and printing is performed with the laser exposure amount of P (L11), printing is performed with the gradation characteristic indicated by the set gradation curve (2). In this manner, the conversion is performed for the other image input levels, and the gradation correction data (3) indicating the relationship between the image input level and the laser exposure amount for realizing the set gradation curve (2) is obtained. Calculate.
(D) The correction curve thus obtained is stored in the RAM 204, and is reused when the same gradation is set.
In the above description, the case where the gradation curve is set from the operation panel 221 has been described. Thus, gradation correction data can be obtained.
[0031]
(H) Printer control flow
FIG. 21 shows a main flow of the printer control unit 201. First, after performing the initial setting (S1), key input processing of the operation panel 221 is performed (S2, see FIG. 22), and the process waits until the start key 304 of the operation panel 221 is pressed (S3). When the start key is pressed, a sensor input process is performed (S4).
Next, input signals from various switches of the operation panel 221 are taken into the RAM in the printer control unit 201 (S5).
Next, the light amount level of the semiconductor laser 264 is set by switching the gain of the gain switching circuit 255 of FIG. 6 according to the set values obtained in steps S4 and S5 (S6).
[0032]
Next, AIDC measurement processing is executed, and the toner adhesion amount is obtained by the AIDC sensor 210 (S7). In the AIDC process, a reference toner image is formed on a photoreceptor, the image reproduction density is detected by the AIDC sensor 210 based on the toner adhesion amount of the image pattern, and is taken into the RAM 204 in the printer control unit 201.
Next, based on the density detection level corresponding to the measured toner adhesion amount, a grid potential correction value, a development bias potential correction value, and an original gradation curve that are set in advance corresponding to this level are selected (S8). ).
Next, the tone correction data shown in FIG. 20 is calculated based on the original tone curve selected in step S8 (S9).
Next, the grid potential V selected in step S8 _G And developing bias potential V _B Then, a printing operation by a known electrophotographic method is executed based on the gradation correction data obtained by the calculation in step S9 until it is completed (S10, S11).
In the case of a color image, one copy is sequentially processed in the order of cyan, magenta, yellow, and black. Therefore, the above-described main flow is repeated for each color.
[0033]
FIG. 22 shows the flow of the key input process (S2 in FIG. 21). First, the input of the shape of the gradation curve is received (S21), and then the input of the degree of the shape is received (S22). Finally, the color balance and the density adjustment value are input from the color balance switch 216 and the operation panel 221 (S23), and the process returns.
[0034]
FIG. _G , V _B , Shows the flow of gradation data selection (S8 in FIG. 21). The grid voltage V based on the detection value level of the AIDC sensor 210 _G , Developing bias voltage V _B Is selected (S41). And (V _G , V _B ) Is selected (S42), and the process returns.
[0035]
(I) Line approximation of gradation data
As described above, in this embodiment, a large number of original tone curves are required in accordance with the level of the AIDC sensor 210. In this embodiment, 8-bit (0 to 255) data is used as the document density data. However, in the calculation, it is handled as 10-bit (0 to 1023) data so as not to lower the precision. To store the gradation curve as a look-up table for such gradation correction conversion requires a large memory capacity.
[0036]
Therefore, in the present embodiment, the capacity can be reduced by storing the basic original tone curve and the selectable tone curve using the polygonal line approximation.
Further, if the gradation correction data calculated from the original gradation curve with respect to the selected gradation curve is also stored using the polygonal line approximation, the memory capacity can be further reduced.
The polygonal line approximation does not store all data corresponding to the image input level (0 to 255), but approximates, for example, a linear polygonal connection of 10 to 20 straight lines. At this time, the curve is stored in the ROM 203 as the applicable range coefficient X (N) (N = 1 to 10) of each straight line, its slope coefficient a (N), and intercept coefficient b (N).
At the time of calculation, first, for image input levels (0 to 255), first, tone correction data (to achieve a tone curve set from an original tone curve stored as a broken line and a set tone curve). (Corresponding to inputs 0 to 255) are sequentially calculated as described above, and are temporarily stored in the RAM 204 as data corresponding to inputs 0 to 255. This may be directly used as the gradation correction data. However, if this is also approximated by a broken line, the memory capacity can be reduced even when the data is stored. Therefore, it is preferable that the calculated data is formed into a polygonal line using coordinates determined based on the absolute value of the value of the second derivative.
[0037]
FIG. 24 shows light emission data f (x) with respect to the image input level (X) on the upper side, and the primary differential value f ′ and the secondary differential value f ″ thereof are shown on the center and lower side.
The second derivative f ″ may be called the rate of change of the slope of f (x), and a place where the value of f ″ (x) is large is a place where the slope of f (x) changes greatly. be able to. By approximating the broken line with priority given to this portion, the accuracy of the actual tone correction can be improved.
As an example, in FIG. 24, for input levels 0 to 255, regions where f ″ ≦ q and f ″ ≧ p are determined. Then, for example, when the number of contacts of the polygonal line approximation is set to 10 (not including 0), a predetermined priority such as 4 points in the 0 to R region, 4 points in the S to 255 region, and 2 other points is obtained. The number of coordinate points is assigned based on the coordinates, and accordingly, the coordinates are first divided into five equal parts, 0 to R, and X = S, S + (255-S) / 3, S + 2 × (255-S) / 3, 255 , And X = R + (SR / 3), 10 points of R + (2 × SR / 3) are determined. These are connected to the origin 0 in succession with a straight line from the low level side, and the corresponding input data level range X (N), slope a (N), and intercept b (N) are obtained to form a polygonal line approximation formula. These are stored in the RAM.
When the copying operation starts, an exposure output level is obtained from the corresponding a (N) and b (N) according to the input density data from the image reader unit, and a laser is output according to the output.
Note that the priority and how to take p and q may be determined according to the number of polygonal line coordinate points, and the priority may be given particularly to the highlight portion. These may be set separately for each model.
[0038]
In the determination of the second derivative, p and q may be set separately, or | f ″ | may be used to determine only p.
The coordinate determination corresponding to the number of points determined in advance according to the priority has been described. In addition to this, 0 to 255 are divided in advance into areas larger than the final number of contacts, and 2 It is also possible to determine from the coordinates having the large second derivative result f ″. For example, the value of f ″ is calculated every 4 (f ″ (4), f ″ (8), f ″ (12),... F ″) (252)) A method may be used in which nine points (in the case of approximation with ten polygonal lines) excluding the origin 0 and the Max255 level are determined in order from the larger one, and a polygonal line is created by adding them to 0 and 255. It is.
By storing the polygonal line approximation value thus created in the RAM, the same original gradation curve can be repeatedly used when the same original gradation curve is selected.
Also, the original tone curve is approximated by 20 broken lines (20 points excluding the number of contacts 0) and stored in the ROM, whereas the calculated tone correction data is approximated by 10 broken lines.
Making the number of coordinate points of the original tone curve larger than the number of coordinate points of the tone correction data, which is the actual calculation result, leads to an improvement in calculation accuracy.
[0039]
(J) Use of external storage device
The gradation curve can be input from an external storage device such as an IC card. In the operation panel 221 shown in FIG. 5, two IC cards can be inserted into the insertion ports 311 and 312.
The memory configuration of the IC card is configured according to the type of the main body.
FIG. 25 and FIG. 26 show the external appearance and internal configuration of the IC card. Here, the conductive portion 131 is printed on the IC card main body 130. Power can be supplied from the outside through the conductive portion 131, or data can be transmitted and received through a serial interface with the outside.
The control CPU 132 in the IC card ² It manages the PROM 133 and controls the interface with the outside. E ² Data is held in the PROM 133.
[0040]
FIG. 27 shows a configuration of the internal data 134 stored in the IC card. The internal data 134 is divided into blocks 135 of variable length. Then, program data can be written in each block. As a result, a plurality of programs can be registered in one IC card.
One block 135 is composed of various data as described below. That is, the "header" contains a code indicating the registration / non-registration of the program and the type of the program. The "program name" contains the user's registered name of the program, based on which the user can easily know the program creator, the purpose of the program, and the like. The "model code" contains the code of the model that created the program. The "model characteristic information" contains more detailed characteristic information of the model for which the program was created in order to use the IC card between different models. The "various mode memories" store various copy modes that can be set on the operation panel. By reading this, the mode setting state when this program was created can be faithfully reproduced. As an example, a gradation curve is written in the mode memory. The gradation curve is an arbitrary gradation curve 136 and any one of several types of gradation curves stored in the ROM 203 of the copying machine main body. One or both of a curve number 137 indicating whether to select a gradation curve is included.
Since the model code is also stored in this manner, it is possible to store the code information of the insertable machine and the gradation curve correction information according to each machine in the IC card. Therefore, gradation data can be supplied to a plurality of machines.
[0041]
In addition to the gradation curve stored in the data ROM 203 of the main body, an additional selectable gradation curve is stored and stored in the IC card, and the additional gradation curve stored in the IC card is stored by inserting the IC card. May be displayed on the operation panel. A large storage capacity is required to store a large number of gradation curves, but the number of gradation curves can be increased by using an IC card which is a memory external to the machine. At this time, the gradation curve can be selected from both the curve stored in the data ROM 203 of the main body and the curve stored in the IC card.
By storing different gradation curves in a plurality of IC cards, the number of gradation curves can be further increased.
Further, the IC card may be provided with a RAM, and the RAM may be provided with a portion for storing gradation curve data created by the main body. Thus, by storing the gradation curve newly created by the above-described editor 160 or the like in the RAM of the IC card, a custom card can be obtained.
[0042]
FIG. 28 shows a configuration of a control system of the operation panel 221. The panel CPU 190 controls the operation panel 221 while controlling the various input / output devices 191 to 198. The copy mode set on the operation panel 221 is sent as an instruction signal to the printer control unit 201 through the interface.
The operation keys 302 to 310, 313, and 314 on the operation panel form a key matrix, and the ON / OFF state is read by scanning the key matrix.
The LCD interface 191 includes an LCD controller, a video RAM, a character generator, and the like, converts display data set by the CPU 190 into data to be displayed on the LCD module 192 of the display unit 301, and causes the LCD module 192 to display the data. .
The IC card interface unit 193 controls IC card units (IC card readers / writers) 194 and 195 corresponding to the two IC card insertion ports 311 and 312, detects insertion of an IC card, discharges an IC card, and the like. Since data is transmitted and received to and from an IC card through a serial interface, the interface control is performed by the IC card interface unit 193 to reduce the load on the CPU 190.
The tablet interface unit 196 controls data transmission and reception with the above-described tablet editor 232 or other editors 140, 150, and 160.
The barcode interface unit 197 analyzes the data read and sent by the barcode reader pen 315 and converts the data into a data format that can be easily processed by the CPU 190.
[0043]
Next, registration of a gradation curve to an IC card will be described. FIG. 29 shows a screen of the display unit 301 for calling data programmed in the IC card. This screen is displayed when an IC card is inserted and when a program call key (not shown) on the operation panel 221 is pressed. On this screen, among the eight types of programs that can be registered in the IC card, the currently registered program is displayed with a number and a title on the left side of the screen. , Only the frame is displayed. Then, when the program is called, the selection cursor may be moved to a place to be called with the cursor key 309 and the enter key 307 of the operation panel 221 may be pressed.
Next, when registering a program in the IC card, the user selects “program registration” on the right side of the screen in FIG. 29 and presses the enter key 307. Then, a title input screen shown in FIG. 30 is displayed. On this screen, enter a title, select "End", and press the enter key 307. Then, the screen for selecting a program registration location shown in FIG. 31 is displayed. Here, when the selection cursor is moved to the place to be registered and the enter key 307 is pressed, a number and a title are added to the place, indicating that the program registration is completed. Here, the programmed contents are all of the mode setting contents of the copying machine at that time. Then, when the program registered in the program is called next time, the same state as when the program is registered can be reproduced.
In this embodiment, two IC cards can be used at the same time, but the method of calling / registering a program is the same in any of the IC cards.
[0044]
Next, selection of gradation data from an IC card will be described.
FIG. 32 shows a gradation curve selection screen when one IC card is set. Eight types of arbitrary gradation curves created by the user can be registered in the IC card for each program. Then, on this screen, the user can select from a total of nine gradation curves, four of which and five of the main body standard.
FIG. 33 shows a gradation curve selection screen when two IC cards are set. On this screen, a menu is displayed for each of four types of gradation curves registered in each IC card, and a gradation curve can be selected from the menu.
[0045]
FIG. 34 shows an input example using a barcode. The barcodes shown in FIG. 34 are attached below five types of image quality samples such as flowers, people, fruits, color characters, and dark pictures, respectively, from the left. By reading, a gradation curve corresponding to the selected image quality can be set.
Further, as shown in FIG. 35, a sample diagram (a landscape image in this example) may be added to the IC card 130. This facilitates selection of image quality by the user.
[0046]
【The invention's effect】
If there are a target gradation curve number N and an image density control number M, an N × M gradation curve number is required for each color. Even if the storage capacity is reduced by a polygonal line approximation or the like, a large storage capacity is required. However, according to the present invention, since the tone correction curve is calculated each time from the target curve data and the basic tone data to calculate the light emission correction data, a large storage capacity is not required.
Fine adjustments can be made to the deviation of the gradation characteristics of the entire copying apparatus by switching the basic gradation characteristic data.
The storage capacity can be significantly reduced by calculating and calculating at the time of control without storing all gradation characteristic data.
For example, the storage capacity can be significantly reduced by storing the gradation characteristics in a polygonal line approximation. By storing the additional target gradation curve in the external memory, the range of selection is expanded. It becomes possible to provide a gradation conversion function corresponding to different machines. By storing the newly created gradation curve in an external memory card, a custom card can be created.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating an entire configuration of a digital color copying machine.
FIG. 2 is a block diagram of an image signal processing unit.
FIG. 3 is a block diagram of a part of a printer control unit.
FIG. 4 is a block diagram of a part of a printer control unit.
FIG. 5 is a perspective view of an operation panel.
FIG. 6 is a block diagram of image data processing in a printer control unit.
FIG. 7 is a diagram schematically illustrating an arrangement of a charging charger and a developing device around a photosensitive drum.
FIG. 8 is a diagram of sensitometry in reversal development.
FIG. 9 is a diagram showing how to obtain standard tone correction data.
FIG. 10 is a diagram schematically illustrating a concept of a target gradation curve shape and a stage of the shape change.
FIG. 11 is a diagram of a screen for selecting a type of a gradation curve.
FIG. 12 is a diagram of a screen for selecting a level of a gradation curve.
FIG. 13 is a diagram of a panel of a tablet editor.
FIG. 14 is an input device of a gradation curve by dial setting at low density and high density.
FIG. 15 is a diagram showing a gradation curve selected by the dial setting in FIG. 10;
FIG. 16 is an input device of a gradation curve by dial setting at low density and high density.
FIG. 17 is a diagram of an input device using keys for setting a center, a low density, and a high density.
FIG. 18 is a diagram showing an input method that can be set at arbitrary break point coordinates.
FIG. 19 is a diagram showing data stored for light emission data calculation.
FIG. 20 is a diagram showing calculation of light emission data.
FIG. 21 is a diagram showing a main flow of a printer control unit.
FIG. 22 is a flowchart of a key input process.
FIG. 23 _G , V _B Is a flowchart for selecting a gradation.
FIG. 24 is a diagram showing light emission data on the upper side, and first and second derivative values of the light emission data on the center and the lower side.
FIG. 25 is an external view of an IC card.
FIG. 26 is a diagram of an internal configuration of an IC card.
FIG. 27 is a diagram showing a configuration of internal data stored in an IC card.
FIG. 28 is a diagram of a configuration of a control system of an operation panel.
FIG. 29 is a diagram of a display screen of a registration program in the IC card.
FIG. 30 is a diagram of a title input screen.
FIG. 31 is a diagram of a selection screen of a program registration place.
FIG. 32 is a diagram illustrating an example of a gradation curve selection screen.
FIG. 33 is a diagram showing an example of a gradation curve selection screen.
FIG. 34 is a diagram illustrating an example of input using a barcode.
FIG. 35 is a diagram of a card provided with a sample diagram.
[Explanation of symbols]
201: printer control unit, 203: data ROM, 204: RAM,
210: AIDC sensor, 232: Tablet editor,
253: γ correction unit, 311, 312: IC card insertion slot,
322, 323: Mode setting keys.

Claims (1)

In a digital image forming apparatus that forms an image based on an input image signal,
Storage means for storing a non-linear basic tone characteristic indicating the relationship between the density level of the input image signal and the density of the image actually printed out ;
Setting means for setting a target gradation characteristic which is a relationship between a density level of an input image signal and a density of an image actually printed out by a user operation ;
From the basic tone characteristics stored in the storage means and the set target tone characteristics, tone correction data indicating the relationship between the density level of the input image signal and the output level for print output is calculated. Computing means for performing
A digital image forming apparatus comprising: a tone correction unit that converts an image signal to be formed based on the tone correction data obtained by the calculation unit and outputs the converted image signal.

Images